This invention relates to electrical boxes, such as outlet or junction boxes, which are used in commercial or residential buildings. More particularly, the invention relates to electrical boxes having a molded non-combustible exterior which precludes the passage of fire and minimizes sound transmission.
The risk of the passage of fire through a wall from one interior space of a building to another through electrical junction boxes is not readily apparent to a layman but is well known to those in the business of fire safety. In many cases, a firefighter's ability to extinguish a fire with minimal damage may depend upon the ability to contain the fire within a relatively small space. While walls may be made of fire resistant material, a rampaging fire may escape through holes in the ceiling or walls frequently used to house electrical boxes. Once the fire penetrates the walls, it may travel rapidly through spaces between the walls into attic or crawl space areas, spreading rapidly. Accordingly, the ability to confine a fire to a single room may depend upon the ability to preclude its travel through electrical fixtures.
Unfortunately, the ability to impede travel of a fire through electrical boxes is often elusive. For example, in the installation of electrical boxes in walls and ceilings, the proper frontal alignment of the face plate of the box is difficult since deformities (knots, splits, checks, or holes) may exist in the framing members to which the box is attached. To compensate for these deformities, it is common to tilt the box at an angle in the wall, resulting in an improper seal around the opening of the box. In addition, the attachment of the box to the wall is frequently not secure. Thus, in the process of fighting the fire, the impact of a water stream from a hose on the electrical box may deform the box, allowing the fire to proceed through the wall.
Another installation problem relates to the use of veneer on walls or floors with various types of tile, brick, paneling, or similar materials. Where these veneers are of uneven thickness, deformities exist around the opening of the outlet which leave cracks and frequently cause warpage of the outlet coverage even causing breakage of these covers. In addition, it is frequently necessary to position the electrical outlet in the wall taking into account the thickness of the wall treatment that will ultimately be mounted on the wall. If the box is mispositioned in the wall such that the face of the box protrudes through the surface of the wall sheathing, either the sheathing may have to be removed and the box repositioned, or a metal spacer may be placed around the wall opening in order to extend the wall surface to the proper installation depth to permit the electrical box cover to compress snugly against the wall face. Boxes installed in this manner may be easily dislodged or broken in the event of a blow or impact on the face of the box.
Another typical danger is caused by the over-tightening of mounting screws for ceiling-mounted lamps, causing the electrical box in the ceiling to become tilted. This may cause weakening of the mounting bracket, or even extraction of the nails holding the box to the framing members, destroying any caulking used to seal the box and attenuate sound.
In addition to fire resistance in apartment, hotel, condominium, and similar buildings, it is desirable to provide as much sound resistance as possible between the various dwelling units to protect the privacy of its occupants. Regardless of thickness of wallboard or quantity of insulation between the walls, sound will travel through the openings made in walls for electrical outlet boxes, particularly through small cracks or holes in the conventional electrical boxes that are used in the construction of these facilities.
The present invention provides an electrical box having a conventional interior housing and a relatively thick, integral (one piece) sheathing molded to the housing and fabricated from a fire resistive material such as mica, silica, plaster of paris, or fiberglass, or various intumescent paints and materials. The entire unit is factory produced and presealed, with no cracks or holes existing in the unit. A pair of conduits extend through walls in the box in order to enable passage of electrical conduit into and out from the box. A collar portion of the sheathing extends outwardly from the front of the box, and is easily machined or otherwise cut away to conform to the wall surface. A special mounting bracket which may accommodate outlets of different sizes or different mounting techniques is also provided. In a preferred embodiment, the unit is provided with a relatively dense foam backing which is used to absorb impact to the face of the box. The electrical boxes of the invention make it virtually impossible for a fire to pass through the box and into another room of a building, and also permit easy adjustment of the box to fit a wall and wall veneer of virtually any thickness.
Various methods have been tried in the past for increasing the fire resistivity of electrical junction boxes. For example, in Moll, U.S. Pat. No. 3,720,783, a cover member is provided for a junction box which forms a tubular collar which can be broken away along a series of lines of weakness in order to conform the front of the junction box with the wall surface. This collar is simply attached mechanically to the front of the electrical box. A similar collar attachment is shown in Hitchcock, U.S. Pat. No. 4,087,624, where a collar of adjustable size is attached to the junction box. In addition, it is known to insulate the interior of various housings with a fire-resistant coating, such as asbestos, as is shown in Cole, U.S. Pat. No. 3,646,244, Palmer, U.S. Pat. No. 4,307,813, and Hune, U.S. Pat. No. 4,413,683.
Accordingly, it is an object of the present invention to provide a factory-manufactured electrical box having an integrally molded fireproof sheathing. It is yet another object of the invention to provide an electrical box having a one-piece molded exterior having a front tubular collar which is easily cut to conform to a wall surface. It is yet another object of the invention to provide a molded electrical box in combination with a mounting bracket adapted to mate with the components of the electrical box, which bracket serves to rigidly mount the electrical box in a wall while permitting slight variations in the attitude of mounting the box. It is yet a further object of the invention to provide an electrical box which minimizes the potential for transport of fire and sound through the box or the opening in the wall cut for the box. These and other objects of the invention will be obvious from the following description of a preferred embodiment thereof.